Method of producing 1,1,1,2,2-pentafluoroethane a method of producing 2,-2,-diohloro-1,1,1-trifluorethane and a method of purifying 1,1,1,2 pentafluoroethane

ABSTRACT

A production method in which reaction processes are divided into two regions comprising one reaction region where mainly perchloroethylene is made to react with HF in a vapor phase in the presence of a catalyst and the other reaction region where HCFC-123 (CF 3 CHCl 2 ) and/or HCFC-124 (CF 3 CFHCl) is made to react with HF in a vapor phase in the presence of a catalyst, the former region being kept at a higher pressure and the latter region at a lower pressure during the reaction procedure. By this method it is possible to keep the conversion of perchloroethylene at a high level while securing the life of a catalyst, and it is also possible to raise the selectivity of HFC-125. This is a method of producing HFC-125 in which the content of CFC-115 is lowered to not more than 15 vol % of the total amount of HFC-125 and CFC-115, and then CFC-115 is made to react with hydrogen in the presence of a catalyst. By this method, reaction conditions can be lightened and the absolute amount of by-products also decreased, and the effective purification of HFC-125 can be realized.

This application is a continuation of prior application Ser. No.09/023,811 filed Feb. 13, 1998, which is a division of prior applicationSer. No. 08/513,755 filed Sep. 5, 1995, which is a continuation-in-partof PCT/JP94/00348 filed Mar. 3, 1994.

A method of producing 1,1,1,2,2-pentafluoroethane, a method of producing2,2-dichloro-1,1,1-trifluoroethane, and a method of purifying1,1,1,2,2-pentafluoroethane.

INDUSTRIAL FIELDS WHERE THE INVENTION CAN BE UTILIZED

This invention relates to a method of producing1,1,1,2,2-pentafluoroethane that is useful as a substitute for freonsand is expected to serve as a refrigerant, a method of producing2,2-dichloro-1,1,1-trifluoroethane, and a method of purifying1,1,1,2,2-pentafluoroethane.

PRIOR ART

1,1,1,2,2-pentafluoroethane (HFC-125) is expected to be applied as arefrigerant and is also useful as a substitute for freons.

In recent years, under circumstances whereby freons are regulated, thereduction plan for HCFCs has been determined after that of CFCs. Atpresent, HCFC-22 (CHClF₂) that is a kind of HCFC, is widely used as arefrigerant. It is therefore useful to determine and produce asubstitute for HCFC-22. As its possible substitutes, HFC-32 (CF₂H₂),HFC-152a (CH₃CHF₂), HFC-143a (CH₃CF₃), HFC-134a (CF₃CH₂F), and HFC-125are proposed. This invention relates to a method of producing HFC-125,one of the proposed substitutes.

As production methods of HFC-125, some reactions have been known:fluorination of perchloroethylene (Jap. Pat. Publication No. 17263/1964,U.S. Pat. No. 4,766,260); fluorination of HCFC-122 (Jap. Pat. OpeningNo. 172932/1990, Jap. Pat. Opening No. 29940/1992); fluorination ofHCFC-123 (Jap. Pat. Opening No. 226927/1992, WO92/16482, EP513823); andreduction of CFC-115 (Jap. Pat. Opening No. 258632/1989). This inventionrelates to the reaction process of producing HFC-125 by fluorinatingperchloroethylene.

As a method of producing HFC-125, it is reported that the fluorinationreaction of a perchloroethylene as a starting material, especiallyperchloroethylene, is conducted at a temperature from 350° to 380° C. inthe presence of a chromium-oxide catalyst (Jap. Pat. Publication No.17263/1964). In Jap. Pat. Opening No. 178237/1990, reactions have beenimproved by changing catalysts. According to the improvement, theconversion of perchloroethylene has been raised, but the selectivity ofHFC-125 still remains at a low level of about 15%. As shown inWO92/16479, the low selectivity is unchanged even if the catalyst ischanged to one based on Zn.

Like this, in reactions using perchloroethylene as a raw material, theconversion of perchloroethylene has been improved. It cannot, however,be sufficiently confirmed at present whether technology to improve theselectivity of HFC-125 together with its conversion has been achieved.

Accordingly, a reaction starting from HCFC-123(2,2-dichloro-1,1,1-trifluoroethane) has been proposed. In Jap. Pat.Opening No. 226927/1992; it is shown that HCFC-124(2-chloro-1,1,1,2-tetrafluoroethane) and HFC-125 can be obtainedselectively by using a chromium catalyst having an valence number ofthree or more. In WO92/16482, a reaction with a catalyst mainlycomprised of Zn is explained, showing a result of the high selectivityof HCFC-124. In EP513823, a reaction with a chrom-manganese catalyst isattempted. In any case, these proposals are aimed at a high yield ofHFC-125 by improving their catalysts.

When HFC-125 is produced, 1-chloro-1,1,2,2,2-pentafluoroethane (CFC-115)is formed as an impurity, for example, in the process of producingHFC-125 by fluorinating perchloroethylene.

Inasmuch as CFC-115 is one of specified freons whose production must bediscontinued in 1995, it is necessary to lower the content of CFC-115 aslittle as possible in the production of HFC-125. There exists a limit,however, in raising the purity of HFC-125 by rectification becauseHFC-125 and CFC-115 form an azeotrope-like composition.

The reaction itself of reducing CFC-115 to HFC-125 is already known.Jap. Pat. Opening No. 258632/1989 shows that this reaction is conductedby using a catalyst, in which a metal chosen from the platinum and irongroups or from rhenium is carried on active carbon or alumina. Jap. Pat.Opening No. 29941/1992 shows a method to control the formation ofexcessively reduced products. WO91/05752 shows a method of performingthe reaction by changing a kind of catalyst with a catalyst comprised ofa metal chosen from Al, Mo, Ti, Ni, Fe, or Co, on a silicon-carbidecarrier. A reaction by using a palladium catalyst on a carrier from thealumina group is shown in EP506525.

All these known technologies are aimed at decreasing the formation ofexcessively reduced products by improving catalysts to attain a highselectivity of HFC-125. Accordingly, severe selection of a catalyst isneeded to raise reaction activity (conversion) and the product'sselectivity.

OBJECTIVES OF THE INVENTION

A purpose of this invention is to offer an HFC-125 production methodthat can attain not only a high conversion of perchloroethylene used asa starting material but also a high efficiency in HFC-125 production.

Another purpose of this invention is to offer a method of efficientlyproducing an HCFC-123 that can be used to produce HFC-125.

A further purpose of this invention is to offer a purification methodenabling to produce HFC-125 efficiently and with high selectivity whilemitigating the reaction conditions, including the selection of acatalyst in connection with the conversion and selectivity of thereaction.

THE CONSTITUTION OF THE INVENTION

The inventors found that high pressure and high temperature areeffective to increase the conversion of perchloroethylene, and that lowpressure and high temperature are effective to improve the selectivityof HFC-125. Accordingly, the increase in pressure will exert conflictingeffects on the reaction processes of directly producing HFC-125 byfluorinating perchloroethylene. Furthermore, the increase in reactiontemperature that is a common condition to improve the yield of HFC-125has a detect that may cause catalytic deterioration. Under theseconditions the inventors ascertained the reaction process for theeffective formation of HFC-125, having created this invention.

This invention thus relates to the method of producing1,1,1,2,2-pentafluoroethane (HFC-125) in which reactions are conductedin two reaction regions. In the first reaction regions mainlyperchloroethylene reacts with hydrogen fluoride in a vapor phase in thepresence of a catalyst. In the second reaction region, mainly2,2-dichloro-1,1,1-trifluoroethane (HCFC-123) and/or2-chloro-1,1,1,2-tetrafluoroethane (HCFC-124) react with hydrogenfluoride in a vapor phase in the presence of a catalyst. The firstreaction region is kept at a higher pressure than the second reactionregion.

In the reactions of forming HFC-125 by fluorinating perchloroethylenewith hydrogen fluoride, the reaction processes of this invention aredivided into two reaction regions. One region is where mainlyperchloroethylene reacts with HF in a vapor phase in the presence of acatalyst. The other region is where mainly HCFC-123 (CF₃CHCl₂) and/orHCFC-124 (CF₃CFHCl) react with HF in a vapor phase in the presence of acatalyst. It is characteristic that the first region is kept at a higherpressure and the second region at a lower pressure while the reactionsproceed to produce HFC-125(CF₃CF₂H).

In the production method based on this invention, dividing reactionregions and the difference in their pressure conditions make it possiblein the high-pressure stage to keep the conversion of perchloroethyleneat a high level by securing the catalyst's life through maintaining arelatively low temperature. Conversely, in the low-pressure stage, it ispossible to increase the selectivity of HFC-125 because a reaction canbe conducted at a lower pressure by setting its reaction conditionsindependently from those of the high-pressure stage.

In the fluorination reaction of perchloroethylene, it is first necessaryto use a catalyst of high activity to improve the conversion ofperchloroethylene. With such a catalyst, increasing the temperature,maintaining a long contact time, raising the mole ratio of HF toperchloroethylene, and increasing the pressure are required further toimprove the conversion by changing reaction conditions. As for theconversion of perchloroethylene, maintaining a high-pressure conditionwill exert an effect on promoting the reaction.

There exist some defects in each of these factors. For example,increasing the temperature will promote the deterioration of catalysts,although this exerts effects on improving not only the conversion ofperchloroethylene but on the selectivity of HFC-125. Extension of thecontact time will make a reactor large and then necessitate a largeramount of a catalyst. Or if the same reactor is used, it will decreasethe volume of reaction gases, resulting in decreasing productivity.Raising the mole ratio will cause an increased amount of unreacted HF tobe recovered and will raise the volume of flowing reaction gases.Especially, increasing the reaction pressure will lead to an increase inperchloroethylene conversion, and also to diminution in the selectivityof target HFC-125 what is worse. This will result in a decrease in theyield of HFC-125.

A reaction process that can solve these defects and make the use of theabove-mentioned advantages was offered for the first time by thisinvention. The process is thus divided into two reaction regions whereIn the first region perchloroethylene reacts with HF in a vapor phase inthe presence of a catalyst and in the second region HCFC-123 and/orHCFC-124 react with HF in a vapor phase in the presence of a catalyst.The former region will be kept at high pressure and the latter will bekept at a lower pressure as reactions proceed.

In this case, the conversion of perchloroethylene can be increased byapplying high pressure. For instance, when the conversion ofperchloroethylene at 5 kg/cm² is compared with that at atmosphericpressure, the ratio is about 1.5 times at 330° C. Pressure in thehigh-pressure-reaction stage is recommended to be from 3 kg/cm²G to 30kg/cm²G, or preferably from 5 kg/cm²G to 15 kg/cm²G.

Because the purpose of this high-pressure-reaction stage is to formmainly HCFC-123, the temperature increase needed to improve theselectivity of HFC-125 can be avoided. These two factors for temperaturediminution will work toward suppressing the deterioration of catalysts.This is a very advantageous point for dividing reaction stages.Moreover, CFC-1111 (CCl₂═CClF), CFC-1112a (CCl₂═CF₂), and HCFC-122(CHCl₂CClF₂) are acceptable as reaction gases in this reaction stage.

It was meanwhile found that high-pressure conditions suppress thefluorination reactions of HCFC-123 and HCFC-124 and decrease theselectivity of HFC-125. For example, when the conversion of HCFC-123 andthe selectivity of HFC-125 at a pressure of 5 kg/cm² are compared withthose at atmospheric pressure, the ratios at 330° C. will be 3:4 and1:2, respectively.

It is therefore known that lowering reaction pressure is preferable toraising the yield of HFC-125. Moreover, the formation ratio of chlorinecontaining undesirable by-products, for example, HCFC-133a (CF₃CH₂Cl),CFC-114a (CF₃CFCl₂), and CFC-115 (CF₃CF₂Cl) to the targeted productHFC-125 will diminish under lower-pressure conditions. From these pointsof view, the process of this invention is highly advantageous. This isbecause in the low-pressure stage, pressure can be lowered to the levelapproximating equipment-pressure losses. Pressure in thelow-pressure-reaction stage is recommended to be not more than 5 kg/cm²,or preferably to be lnot more than 3 kg/cm²G.

Furthermore, catalytic deterioration becomes relatively slower in thefluorination of HCFC-123 and thereafter. Accordingly, in the latterreaction stage, reaction temperature can be kept higher than that innon-dividing of the reaction region. This results in the advantage ofincreasing HFC-125's selectivity. For instance, the selectivity ofHFC-125 will be increased by about 2.5 times by raising the temperatureof fluorinating HCFC-123 from 330° C. to 350° C.

From the above-mentioned viewpoints, the advantages of dividing reactionstages and of adopting different reaction pressures for each stage are(a) extension of the lifetime of catalysts as well as (b) increase inyield of HFC-125.

As mentioned above, temperature in the high-pressure-reaction stage isgenerally lower than in the low-pressure-reaction stage. Propertemperature ranges will range from 200° to 450° C. (preferably from 250°to 400° C.) in the former stage, and from 250° to 500° C. (preferablyfrom 300° to 450° C.) in the latter stage.

The ratio of hydrofluoric acid to the organic compound (mainlyperchloroethylene) to be supplied to the high-pressure-reaction stageshould be from 2 to 20 in its mole ratio (preferably from 3 to 15). Theratio for the low-pressure-reaction stage should be from 2 to 20(preferably from 2 to 15). The proper contact time will be from 60 to7200 in SV for both stages (preferably from 120 to 3600).

Generally known fluorination catalysts are acceptable as catalysts forthe reaction (the high-pressure-reaction stage and/or thelow-pressure-reaction stage). But even more preferable catalysts are achromium-oxide catalyst having a surface area of not less than 170 m²/g(see EP514932), a catalyst comprised of chromium oxide having a surfacearea of not less than 170 m²/g and at least one element chosen from Ruand Pt (see EP516000), or a catalyst comprised of active alumina and atleast one element chosen from Sn, Mo, V, Pb, Ti, Zr, and Ge.

The two reaction stages may be connected directly. It will be moreadvantageous, however, to have a distillation column between the twostages. That is, if reaction gases flow continuously from thehigh-pressure-reaction stage to the low-pressure-reaction stage, the HClformed in the high-pressure-reaction stage, and the unreactedperchloroethylene, are ready directly to flow in thelow-pressure-reaction stage maintained at a high temperature. In thiscase, HCl exerts an adverse effect on the fluorination reaction.Unreacted perchloroethylene causes catalytic deterioration in thelow-pressure-reaction stage. If reaction gases continuously flow fromthe low-pressure-reaction stage to the high-pressure-reaction stage, theamount of HFC-125 formed in the low-pressure-reaction stage decreases inthe high-pressure-reaction stage.

Accordingly, the removal of unnecessary gases for reaction bydistillation columns (a) between the high- and low-pressure-reactionstages, and (b) after the low-pressure-reaction stage, is considered tobe effective to avoid the defects of the continuous inflow of reactiongases. The installation of distillation columns will enable theadvantage whereby the ratio of HF to organic compounds—both to besupplied to each reaction stage—can be set independently. From thedistillation column in the high- or low-pressure-reaction stages,unreacted raw materials and by-products (for example, CFC-1111,CFC-1112a, HCFC-122, and HCFC-124) can be recycled to correspondingreaction stages.

Although consideration was given to installing two distillation columnsas mentioned above, it is of course possible to install only one column.In such a case, the column is used in such a way that each gas in andout the high- and low-pressure-reaction stages is introduced in ordischarged from one distillation column. As an instance of use of thistechnique, the following is practicable. Liquid drawn from an area inthe distillation column where the main compound is perchloroethylene isset at a specified pressure by pumping. The pressurized liquid is mixedwith additional perchloroethylene and HF, and fed into thehigh-pressure-reaction stage. During this process the reaction gas isallowed to be vaporized (a) after or (b) before having been mixed.

A reaction gas from the high-pressure-reaction stage is returned intothe area of the distillation column where organic compounds arecomprised mainly of HCFC-123 and HCFC-124. Although the pressure of thehigh-pressure-reaction stage is considered to be from three to 30kg/cm²G, it its minimum pressure is set at higher than the pressure inthe distillation column, it is unnecessary to pressurize the reactiongas for its return into the distillation column. This constitutes anequipment advantage.

Furthermore, a gas drawn from an area in the distillation column whereorganic compounds are comprised mainly of HCFC-123; and/or a gas drawnfrom an area where organic compounds are comprised mainly of HCFC-124;are mixed to be introduced into the low-pressure-reaction stage afteradjusting the content of HF if necessary. In this case, it is better tonix additional HF with the gas drawn from the distillation column afterreducing the pressure of the gas. It is unnecessary, however, tocontinue to adjust the gas pressure. The composition of a gas drawn fromthe distillation column can be adjusted in accordance with the contentof HCFC-124 in the distillation column. Thus, in either reaction stage,even if the products composition is changed to some extent because ofchanges in the reaction conditions, the composition of components in thedistillation column can be adjusted by this extraction method.

Reaction gases from the low-pressure-reaction stage are pressurizedafter being liquefied, or in the gas state as they are, or in bothstates. The gases can then be returned to an area in the distillationcolumn where organic compounds are comprised mainly of HFC-125 andHCFC-124. The ratio of HF to organic materials to be supplied to eachreaction stage can be set up independently even if the process isconducted using one distillation column. Thus, even if one distillationcolumn is used, each of the two reaction stages can be operated so as tohave practically independent reaction conditions.

From the top of the distillation column, principally HFC-125 and HCl areextracted and sent to the purification process. The recycling ofunreacted perchloroethylene is conducted, for instance, by being mixedwith HF and reintroduced into the high-pressure-reaction stage afterreturn to the distillation column.

The materials used in both reaction stages, incidentally, are preferablyhydrofluoric-acidproof materials. Hastelloy and Inconel are preferableexamples.

Furthermore, according to this invention, HFC-125 can be produced bymaking principally HCFC-123 and/or HCFC-124 react with hydrogen fluorideat low pressure in a vapor phase and in the presence of a catalyst. Inthis reaction, the pressure had better been kept at not more than 3kg/cm²G and the temperature at between 250° and 500° C.

As mentioned above, it is desirable to use a chromium-oxide catalysthaving a surface area of 170 m²/g or more, a catalyst comprised ofchromium oxide having a surface area of 170 m²/g or more, and at leastone element chosen from Ru and Pt, or a catalyst comprised of activealumina and at least one element chosen from Sn, Mo, V, Pb, Ti, Zr, andGe.

Mostly HCFC-123 can be obtained by mainly causing perchloroethylene toreact with hydrogen fluoride in a vapor phase in the presence of acatalyst, at a pressure of between 5 kg/cm²G and 15 kg/cm²G, and at atemperature between 200° and 450° C. In this case it is desirable to usethe same catalyst as mentioned above.

This invention also relates to a method of purifying HFC-125, in whichCFC-115 is removed by being converted to HFC-125 by making a gas mixturewhich contains 1,1,1,2,2-pentafluoroethane (HFC-125) and1-chloro-1,1,2,2,2-pentafluoroethane (CFC-115) or not more than 15volume percent of the total pentafluoroethane react with hydrogen in avapor phase in the presence of a catalyst.

This invention relates to a method of purifying HFC-125 thatcharacteristically removes the CFC-115 contained in HFC-125 by causingCFC-115 to react with hydrogen in a vapor phase in the presence of acatalyst to convert to HFC-125. Employing the method of this invention,the purification of HFC-125 can be conducted effectively becauseCFC-115, an impurity, is converted into the target product HFC-125 byvapor-phase reaction.

Compared with the case where CFC-115 is independently reduced to formHFC-125, the method of this invention has the additional characteristicsof being able to select inferior conditions (catalysts, temperature,etc.) in activity (conversion) and selectivity. Accordingly, no specificcatalyst is required for this reaction, but general reduction catalystscomprised of an element of Group VIII, including palladium and rhodium,can be used.

In the method of this invention, the gas mixture in which HFC-125, areduction product of CFC-115, is contained in greater quantity thanCFC-115 is called the reaction gas. When CFC-115 is reducedindependently, 1,1,1,2-tetrafluoroethane (HFC-134a) and1,1,1-trifluoroethane (HFC-143a)—further reduced products thanHFC-125—are created as impurities. Accordingly, in the method of thisinvention, it was predicted that simultaneously while CFC-115 is beingreduced to HFC-125, the HFC-125 in the introduced gas is further reducedto create a large quantity of HFC-134a and HFC-143a.

It was found, however, that the hydrogenation reaction of HFC-125 doesnot easily proceed when HFC-125 alone is reacted with hydrogen. Thus,when HFC-125 is produced by the reaction of CFC-115 and hydrogen,further hydrogenated compounds (HFC-143a, HFC-134a) are produced. When,however, the reaction of HFC-125 and hydrogen is conducted under thesame conditions, the formation of further hydrogenated compounds(HFC-143a and HFC-134a) was found to be much lowered.

This means that in the reaction of hydrogen with a gas mixture (in whichHFC-125 is a main component and the content of CFC-115 is small),HFC-125 hardly reacts and only CFC-115 is reduced. Elucidating this facthas made available for the first time the ability to eliminate CFC-115in HFC-125 by reducing the mixture.

According to the method of this invention, inasmuch as HFC-125 is themain component and CFC-115 is controlled at not more than 15 volumepercent of the total amount of HFC-125 and CFC-115, it is possible touse a catalyst whose selectivity is inferior to that of a catalyst to beused in the reduction reaction of CFC-115 alone. When the proportion ofCFC-115/(CFC-115+HFC-125) is not more than 0.15, the absolute amount ofby-products becomes not more than 0.15 times that in the reaction ofCFC-115 alone because HFC-125 minimally reacts and almost allby-products are caused by CFC-115.

Accordingly, the method of this invention can purify HFC-125 efficientlybecause when CFC-115 is converted to the target product HFC-125 byvapor-phase reaction, the amount of produced by-products is small andpostconversion treatment will be eliminated in such an amount.

When HFC-125 is produced by the reduction of CFC-115, it isindispensable to set up a reaction condition so that a conversion ofnearly 100% can be attained. This is because if the conversion isdecreased, the diminished portion is directly related to the increase ofCFC-115. Simultaneously, conditions are needed to improve theselectivity of HFC-125. Accordingly in this case, severe reactionconditions or catalysts that have excellent activity and selectivity areneeded. In the reaction in this invention, the severity of the reactionconditions, including catalysts, can be somewhat lightened because theinitial concentration of CFC-115 is low and HFC-125 is hard to react.

This constitutes a great difference between the reaction in thisinvention and the reduction reaction of CFC-115 alone. Accordingly,inasmuch as catalysts for the reaction have no special restriction inthe method of this invention, general-reduction catalysts can be usedthat are comprised of an element of Group VIII, including palladium andrhodium. Moreover, compared with the case where CFC-115 gas isindependently reduced to form HFC-125, the method of this invention canselect inferior conditions (catalysts, temperature, etc.) in activity(conversion) and selectivity.

As catalysts for the method of this invention, general-reductioncatalysts can be used in which a metal chosen from the elements of GroupVIII, including palladium and rhodium, are carried with alumina oractive carbon. The selectivity of HFC-125 is increased when an aluminacarrier is used. Catalysts whose selectivity is too low are undesirable.It is better to use, for example, a catalyst having not leas than 80%selectivity. Furthermore, it is also possible to use a palladiumcatalyst that is carried on a carrier and added with at least one metalchosen from vanadium and zirconium. It is desirable, however, to use acatalyst and reaction conditions to ensure that the conversion ofCFC-115 is 95% or more in the reaction of CFC-115 alone with hydrogen,and that a selectivity of HFC-125 is 80% or more.

In the method of this invention, the content of CFC-115 in the gasmixture of HFC-125 and CFC-115 is preferably less than 15 volumepercent. This is necessary to make the most of the above-mentionedadvantages. If the content exceeds that value, it would be better to usethis method after diminishing the content by purification of the gasmixture.

The amount of hydrogen necessary to reduce CFC-115 to HFC-125 can bechanged depending on the reactivity of CFC-115 (CFC-115 content).Generally, the amount of hydrogen is preferably from 0.5 to 1000 at theratio of H₂:CFC-115.

The reaction temperature of CFC-115 with hydrogen in this invention ispreferably from 170° to 400° C. If the temperature is too high,excessively reduced products such as HFC-134a (CF₃CFH₂) and HFC-143a(CF₃CH₃) are output. Especially, the formation of HFC-143a isundesirable because its boiling point is −47.6° C. and is so close tothat of HFC-125 (−48.5° C.) that it is very difficult to separate onefrom the other. Furthermore, if the reaction temperature is too low, thereaction is hard to proceed.

Although HFC-125 is known to be produced by fluorinatingperchloroethylene (Jap. Pat. Publication No. 17263/1964), CFC-115 isgenerally formed as a by-product in this known method. Accordingly, thecrude-gas postreaction contains HF and HCl gases. The presence of thesegases itself does not always disturb the reaction of CFC-115 andhydrogen in the method of this invention. It is preferable, however, forthe process to conduct the reaction after removing these acids.Furthermore, it is more effective from the viewpoint of the process orthe product distribution to use gases purified to HFC-125 and CFC-115 asreaction gases, but this composition should not always be followed.

Moreover, in the reaction to produce HFC-125 by the reduction ofCFC-115, unreacted CFC-115 exists as an impurity in HFC-125. In such acase, when the content of CFC-115 is not less than 15% of the totalamount of CFC-115 and HFC-125, it is better to supply the mixture tothis reaction after its rectification.

As mentioned above, when HFC-125 is produced by making the products inthe first reaction region (HCFC-123 and/or HCFC-124) react further withHF in the second reaction region, or by making HCFC-123 and/or HCFC-124react with HF, CFC-115 is also output actually as a by-product togetherwith the target product HFC-125 in the second reaction region orpostreaction. It is thus desirable for the effective production ofHFC-125 to remove the CFC-115 by this invention's purification method.Purification conditions in this case may be the same conditions asmentioned above.

The Possibility of Utilizing the Invention in Industry

As mentioned above, this invention has two reaction regions in producingHFC-125, which is a useful substitute for freons, by fluorinatingperchloroethylene. One reaction stage features mainly a reaction ofperchloroethylene and HF, conducted in a gas phase in the presence of acatalyst. The other reaction stage comprises principally a reaction ofHCFC-123 (CF₃CHCl₂) and/or HCFC-124 (CH₃CFHCl) with HF, and is conductedin a gas phase in the presence of a catalyst. Inasmuch as the reactionin the former reaction stage is conducted in a high-pressure conditionand the reaction in the latter stage in a low-pressure condition, it ispossible in the high-pressure-reaction stage to keep the conversion ofperchloroethylene higher by high pressure while ensuring catalyst lifeby a relatively low temperature. In the low-pressure-reaction stage, theselectivity of HFC-125 can also be improved because reaction conditionscan be set up independently from those in the high-pressure-reactionstage, making possible a low-pressure reaction.

Furthermore, according to this invention, because HFC-125 is the maincomponent and the amount of CFC-115 is maintained at not more than 15volume percent of the total amount of HFC-125 and CFC-115, catalysts maybe permitted to have less selectivity than those needed for thereduction reaction of CFC-115 alone. This means that reaction conditionscan be lightened regarding the conversion of CFC-115 and the selectivityof HFC-125.

Then, inasmuch as almost all by-products are derived from CFC-115because HFC-125 reacts only minimally, and because the ratio of CFC-115to (CFC-115+HFC-125) is kept at not more than 0.15, the absolute amountof by-products will be not more than 0.15 times that in CFC-115 alone.Because of this, as well as the fact that CFC-115 is converted to thetarget product, it is possible effectively to purify HFC-125.

EXAMPLE

This invention will be explained in the following examples withcomparative cases. The following examples do not restrict this inventionbut a variety of modifications will be possible based on their technicalconcepts.

Example 1

Nine hundred grams of chromium-oxide catalyst having been treated byfluorination (fluorine content 29%) were infused into Reactor A made ofHastelloy 25A. Keeping the pressure in the reactor at 5 kg/cm2, a mixedgas of hydrofluoric acid (24.7 l/in.) and perchloroethylene (1.9 l/min.)was supplied at a temperature of 330° C. The conversion ofperchloroethylene was 62% and the selectivity of HCFC-123, HCFC-124, andHFC-125 was 58%, 21%, and 5%, respectively.

Then the produced HCFC-123 (0.68 l/min.) and HF (8.84 l/min.) wereintroduced into Reactor B made of Hastelloy 25A at atmospheric pressureand at a temperature of 350° C. The reactor was filled in advance with320 g of chromium oxide catalyst, having been treated by fluorination(fluorine content 29%). In this case the conversion of HCFC-123 was 82%and the selectivity of HCFC-124 and HFC-125 were 34% and 65%,respectively. The yield of HFC-125 was 22%.

Comparative Example 1

When the reaction was conducted under the same conditions as in Example1, except that the pressure of Reactor B was changed to the samepressure as Reactor A, the conversion of HCFC-123 in Reactor B was 72%,and the selectivity of HCFC-124 and HFC-125 was 54% and 45%,respectively.

The yield of HFC-125 was 11.6%. The yield of HFC-125 was found to bediminished greatly when a high-pressure condition was used in Reactor B.

Comparative Example 2

Nine hundred grams of chromium-oxide catalyst having been treated byfluorination (fluorine content 29%) were infused into Reactor A made ofHastelloy 25A. Maintaining the pressure in the reactor at atmosphericpressure, a mixed gas of hydrofluoric acid (24.7 l/min.) andperchloroethylene (1.9 l/min.) was supplied at a temperature of 330° C.The other conditions were the same as in Example 1.

In this example the conversion of perchloroethylene was 42%. When thepressure in Reactor A was lowered, the conversion of perchloroethylenewas found to be diminished.

Example 2

Ten grams of a catalyst (0.5 wt % Pd on active carbon) were infused intoa reactor with an inside diameter of 20 mm. Then a gas mixture ofCFC-115 and HFC-125 (ratio of CFC-115 to HFC-125 at 3.5:96.5) (4.4ml/min. at 25° C.) and hydrogen (3.1 ml/mn. at 25° C.) were led throughthe reactor at a temperature of 250° C.

In this example the conversion of CFC-115 was 97.5% and the proportionof CFC-115/HFC-125 were decreased from 3.63% to 0.0876%. NeitherHFC-143a nor HFC-134a were detected.

Example 3

When a reaction was conducted in the same manner as in Example 2 exceptthat a gas mixture of CFC-115 and HFC-125 (ratio of CFC-115 to HFC-125at 3.5:96.5) (8 ml/min. at 25° C.), and hydrogen (40 ml/min. at 25° C.)were flowed, the conversion of CFC-115 was 99% and the percentage ofCFC-115 to HFC-125 was decreased from 3.63% to 0.036%. No HFC-143a wasdetected.

Example 4

HFC-125 and hydrogen were led at a temperature of 250° C. through 10 gof a catalyst (0.5 wt % Rh on active carbon) infused into a reactor withan inside diameter of 20 mm, at a rate of 20 ml/min. (at 25° C.) and 100ml/min. (at 25° C.), respectively.

The conversion of HFC-125 was 0.032%. The composition of HFC-125,HFC-143a, and HFC-134a in the produced gas was 99.968%, 0.00%, and0.032%, respectively. The percentages of HFC-143a and HFC-134a toHFC-125 were 0.00% and 0.0324%, respectively.

Comparative Example 3

A reaction was conducted in the same manner as in Example 4 except thatCFC-115 was led instead of HFC-125.

In this case, the conversion of CFC-115 was 20.8% and the selectivity ofHFC-125, HFC-143a, and HFC-134a were 83.6%, 7.74%, and 8.41%,respectively. The percentages of HFC-143a and HFC-134a to HFC-125 were9.26% and 10.04%, respectively.

Whereas HFC-143a and HFC-134a, both excessively reduced produots, wereformed together with HFC-125 in the reduction reaction of CFC-115, itwas found that in the reduction reaction of HFC-125 (Example 4), HFC-125was hard to be reduced. HFC-143a and HFC-134a were thus minimally formedas compared with the reduction of CFC-115.

Example 5

HCFC-123 (52 ml/min.), HCFC-124 (14 ml/min.), and HF (520 ml/min.) wereintroduced into a reactor made of Hastelloy 25A filled with 40 g offluorination-treated chromium-oxide catalyst (fluorine content 29%) atatmospheric pressure and at a temperature of 340° C. The compositionratio of HCFC-123, HCFC-124, and HFC-125 in the produced gas was2.5:11.4:86.1. The amount of produced HFC-125 was 86.1% of theintroduced organic gases.

Example 6

When the outflow gas from Reactor B in Example 1 was purified, thecomponents of the purified gas were CFC-115 and HFC-125. The proportionof CFC-115 to HFC-125 was 1,230 ppm. When this purified gas (8.5ml/min.) and hydrogen (8.5 ml/min,) were led through a reactor with aninside diameter of 20 mm filled with 10 g of a catalyst (5% Rh on activecarbon) at a temperature of 200° C., the conversion of CFC-115 was99.73% and the composition of the outflow organic gases was 99.993% ofHFC-125, 3.3 ppm of CFC-115, 30 ppm of HFC-143a, and 37 ppm of HFC-134a.

What is claimed:
 1. A method of purifying 1,1,1,2,2-pentafluoroethane,in which 1-chloro-1,1,2,2,2-pentafluoroethane is removed by beingconverted to 1,1,1,2,2-pentafluoroethane by making a gas mixture of1,1,1,2,2-pentafluoroethane and 1-chloro-1,1,2,2,2-pentafluoroethane, inwhich the content of 1-chloro-1,1,2,2,2-pentafluoroethane is not morethan 15 vol % of the total amount of these pentafluoroethane, react withhydrogen in a vapor phase in the presence of a catalyst.